1. Field of the Invention
The present invention relates to a sound processing apparatus for processing audio signals that correspond to sound.
2. Description of the Related Art
As an apparatus of this kind, there has heretofore been known a tape recorder or a camera-integrated VTR which records audio signals obtained through a microphone. When sound is recorded outdoors by using the apparatus of this type, however, the microphone picks up the sound of wind in which the microphone is disposed; i.e., so-called wind noise generates.
Since the wind noise chiefly contains low-frequency components, the analog circuit has heretofore been provided with a high-pass filter (HPF) 31 as shown in FIG. 1. When wind is blowing, a switch 34 is operated to remove wind noise.
Another constitution which automatically detects and removes wind noise has been shown in FIG. 2 in which levels of wind noise and of audio signal are detected by detector circuits 46 and 47 through band-pass filters (BPF) 42 and 43, the levels of these signals are compared by a comparator circuit 48, and the time constant of a time-constant circuit 49 is varied depending upon the result of comparison to change over the characteristics of a variable filter 40 in order to remove wind noise.
The above-mentioned conventional sound processing apparatuses, however, involve the following problems.
The apparatus shown in FIG. 1 is simple in constitution, but manipulation of the change-over switch 34 is left to the user. Therefore, an error or delay of the switch operation is likely occur, so the apparatus is not practical.
In the case of the apparatus shown in FIG. 2, wind noise is automatically detected by a means for detecting wind noise. Wind noise is decreased or removed automatically by a variable filter 40 whose characteristics vary depending upon whether the presence of wind noise. However, the variable filter 40, which is constituted by an analog circuit, becomes complex requiring many constituent parts, and makes it difficult to suppress the manufacturing cost and to maintain precision.
Regardless of a difference between these apparatuses, the components of wind noise are concentrated on the lower side of a low-frequency region. Therefore, the filter needs capacitors of large capacitance, which makes it difficult to realize the apparatus in a small size. In the case of an apparatus for processing stereophonic audio signals, in particular, the filters must be provided for the signals of the right and left channels, making it further difficult to accomplish a reduction in the size.
When the entire constitution using a conventional analog filter is modified for processing digital signals, a demerit such as variance can be eliminated but much merit is not expected from the standpoint of cost since the scale of hardware becomes large. Even if it is attempted to carry out this in a software manner by using an arithmetic circuit or the like circuit, the amount of arithmetic operation is so large that the apparatus could not be realized from the standpoint of execution time and limitation in the memory.
Besides, when an audio signal having frequency components similar to wind noise is input at a predetermined level, the above-mentioned conventional detector circuit which simply compares the levels is not capable of discriminating between a wind noise and an audio signal. Moreover, in case the detector circuit has rendered incorrect decision that the input is wind noise, the audio signal to be recorded is removed, which is a problem.